<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
        .box {
            width: 100px;
            height: 2000px;
            background-color: aqua;
        }
    </style>
</head>

<body>
    <div class="box"></div>
    <button>回顶</button>
    <script>
        var but = document.getElementsByTagName("button")[0];
        but.onclick = function() {
            var tim = setInterval(function() {
                document.documentElement.scrollTop -= 500;
                console.log(document.documentElement.scrollTop);
                var num = document.documentElement.scrollTop;
                if (num <= 0) {
                    clearInterval(tim);
                }
            }, 200);
        };
    </script>
</body>

</html>